1. Field of the Invention
The present invention relates to dielectric filters (including dielectric duplexers) and a communication apparatus using such dielectric filters.
2. Description of the Related Art
Dielectric filters are typically formed using a rectangular parallelepiped dielectric block having a plurality of through holes formed therein. The through holes are plated with internal conductors and an external conductor is formed on the outer surface of the dielectric block, thereby forming a plurality of resonators by the internal conductors, the external conductor, and the portion of the dielectric block located between the conductors. Such filters have been used in communication devices which operate in the microwave band.
There are various possible constructions for the external coupling for such resonators, which can be selected according to the characteristics to be obtained. One such arrangement is shown in Japanese patent 2885119 (Japanese Unexamined Patent Application Publication No. 8-18306) wherein an excitation hole is coupled to a desired resonator. The excitation hole extends parallel to the resonator hole. The internal conductor, which is located on the inner surface of the resonator hole, is connected to the external conductor at one of the openings and is connected to an input/output electrode at the other opening. Furthermore, the input/output electrode extends to the mounting surface of the dielectric block, so that surface mounting is possible.
The degree of external coupling via the excitation hole is determined mainly by the spacing between the excitation hole and the resonator hole. Also, the degree of coupling between the adjacent resonators is determined mainly by the spacing between the adjacent resonators. Therefore, the size of the dielectric block is determined by the number of resonator holes which are in turn determined according to the required characteristics of the filter, the strength of coupling between resonators, the strength of external coupling, etc. At the same time, the position of the contact terminals on the circuit board on which the dielectric filter is mounted is designed to be in alignment with the position of the input/output electrodes of the dielectric filter.
When the dielectric filter and/or the dielectric duplexer is to be redesigned to have different characteristics, the position and spacing of its resonator holes and/or excitation holes will normally change. As a result, the position of the input/output electrodes of the filter will normally change. In such a case, it is preferable to redesign the circuit board to ensure that the contact terminals on the circuit board align with the new position of the input/output electrodes on the redesigned dielectric filter.
Unfortunately, this is not always possible. Sometimes the circuit board cannot be changed. In such a case, it is necessary to redesign the filter without moving the location input/output electrodes thereof. In such a case, the pattern of the input/output electrodes on the mounting surface of the filter must conform to the pattern of the contact terminals on the circuit board and not vice versa and there is a high possibility that improvements cannot be made to optimize the characteristics of the filter due to the limitation of the dimensions thereof.
Even where the circuit board can be redesigned, design constraints (e.g., the location of other elements on the circuit board) may limit the positions on which the contact electrodes can be placed such that it is not possible to align the contact electrodes with the position of the excitation holes. In such a case, some provision must be made for offsetting the position of the input/output electrodes relative to the excitation holes.
An object of the present invention is to provide a dielectric filter which obviates the need to change the design of the circuit board when the design of the dielectric filter is to be changed and in which the degree of freedom of design of the dielectric filter is improved. A further object of the present invention is to provide a communication apparatus using such a dielectric filter. To this end, at least one of the excitation holes has an input/output electrode associated therewith, the input/output electrode has a contact portion located on the mounting surface of the dielectric block at a position which is offset from the location of the excitation hole as viewed along the plane of the mounting surface. The input/output electrode also has a connection portion extending from the contact portion to the excitation hole.
According to one aspect of the present invention, the dielectric filter comprises:
a dielectric block having a plurality of outer surfaces including a front surface and a planar mounting surface extending perpendicular to said front surface, said dielectric block including an excitation hole and a resonator hole, both of which extend from said front surface in a direction parallel to said mounting surface;
an excitation hole conductor formed on an inner surface of said excitation hole;
a resonator hole conductor formed on an inner surface of said resonator hole;
an input/output electrode electrically coupled to said excitation hole internal conductor, said input/output electrode including a connection portion located on said front surface and a contact portion located on said mounting surface, said contact portion being offset from said excitation hole as viewed along the plane of said mounting surface; and
an external conductor, which is insulated from said input/output electrode, formed on a plurality of said outer surfaces.
With this construction, the dielectric filter is formed in such a way that the position of the contact portion of the input/output electrode is brought into alignment with the position of the mounting terminal on the circuit board, so that the position of the excitation hole in the dielectric block can be determined according to the required design characteristics of the filter despite non-alignment of the excitation hole and the mounting terminal. This is advantageous both when a new dielectric filter is designed for use on an existing circuit board and when the dielectric filter is designed for a new circuit board but the design constraints of the circuit board limit the permissible positions of the contact terminals on the circuit board.
In several preferred embodiments, a recessed portion is formed on one of the sides of the dielectric block, one end of the excitation hole is opened in the recessed portion, and an electrode for conducting between the internal conductor on the inner surface of the excitation hole and the input/output electrode formed on the mounting surface is formed in the recessed portion. As a result, the case in which an input/output terminal is not disposed in the outer peripheral portion of the dielectric filter can also be dealt with.
In accordance with another aspect of the present invention, the dielectric filter comprises:
a dielectric block having a plurality of outer surfaces including a front surface, a recessed surface which lies parallel to and spaced from said front surface and a planar mounting surface extending perpendicular to said front and recessed surfaces, said dielectric block including an excitation hole which extends from said recessed surface in a direction parallel to said mounting surface and a resonator hole which extends from said front surface in a direction parallel to said mounting surface;
an excitation hole conductor formed on an inner surface of said excitation hole;
a resonator hole conductor formed on an inner surface of said resonator hole;
an input/output electrode electrically coupled to said excitation hole internal conductor, said input/output electrode including a connection portion located on said recessed surface and a contact portion located on said mounting surface, said contact portion being offset from said excitation hole as viewed along the plane of said mounting surface; and
an external conductor, which is insulated from said input/output electrode, formed on a plurality of said external surfaces of said dielectric block.
In accordance with a further aspect of the present invention, the dielectric filter comprises:
a dielectric block having a plurality of outer surfaces including a front surface and a planar mounting surface extending perpendicular to said front surface and a recess formed in said block at the intersection of said front and mounting surfaces, said recess including a recessed surface spaced from and lying parallel to said mounting surface, said dielectric block including a resonator hole and an excitation hole, both of which extend from said front surface in a direction parallel to said mounting surface;
an excitation hole conductor formed on an inner surface of said excitation hole;
a resonator hole conductor formed on an inner surface of said resonator hole;
an input/output electrode electrically coupled to said excitation hole internal conductor, said input/output electrode including a first connection portion located on said front surface and a second connection portion located on said recessed surface and a contact portion located on said mounting surface, said contact portion being offset from said excitation hole as viewed along the plane of said mounting surface; and
an external conductor, which is insulated from said input/output electrode, formed on a plurality of said external surfaces of said dielectric block.
In accordance with a further aspect of the invention, the dielectric filter comprises:
a dielectric block having a plurality of outer surfaces including a front surface and a planar mounting surface extending perpendicular to said front surface and a recess formed in said block at the intersection of said front and mounting surfaces, said recess including a recessed surface spaced from and lying parallel to said mounting surface, said dielectric block including a resonator hole extending from said front surface in a direction parallel to said mounting surface;
a resonator hole conductor formed on an inner surface of said resonator hole;
a coupling electrode formed on said front face and electrostatically coupled to said resonator hole conductor;
an input/output electrode electrically coupled to said coupling electrode, said input/output electrode including a connection portion located on said recessed surface and a contact portion located on said mounting surface, said contact portion being offset from said excitation hole as viewed along the plane of said mounting surface; and
an external conductor, which is insulated from said input/output electrode, formed on a plurality of said external surfaces of said dielectric block.
The present invention is further directed to a dielectric duplexer including the foregoing filters.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.